All of the above can be reasonable, and true. The biggest factor in embalming, and preservation is the condition of the subject to be embalmed, the conditions in which interment will take place. I have conducted many dis interments. I have seen bodies buried more than 20 years still be in very good condition, in Batesville, Aurora and other manufacturers. I have also witnessed the opposite. Embalming is a science. The skill of the practitioner, his/her level of experience and conditions of the deceased are important. Bodies embalmed for medical schools are kept for many years after being embalmed. Look at Lenin, Stalin, the have been on display for decades. Abraham Lincoln's body was recognizable many years after he was embalmed, and he was carted around on a train, and buried in a lead casket. Embalming is only as good as the embalmer, chemicals and techniques used.
John